Misfire detection device and method for internal combustion engine

Abstract

A misfire detection device for an internal combustion engine is configured to execute: a deactivating process that deactivates combustion control for air-fuel mixture in one or some of cylinders; a provisional determination process that uses a detection value of a sensor to output a logical value indicating whether a misfire has occurred; a provisional determination counting process that counts a number of times a specific one of the logical value output by the provisional determination counting process has been output; and an official determination process that makes an official determination of whether the misfire has occurred using, as an input, the number of times counted by the provisional determination counting process during a specific period.

What is claimed is: 
     
       1. A misfire detection device for an internal combustion engine, the internal combustion engine including a sensor and cylinders, wherein
 the misfire detection device is configured to execute:
 a deactivating process that deactivates combustion control for air-fuel mixture in one or some of the cylinders; 
 a provisional determination process that uses a detection value of the sensor to output a logical value indicating whether a misfire has occurred; 
 a provisional determination counting process that counts a number of times a specific one of the logical value output by the provisional determination counting process has been output; and 
 an official determination process that makes an official determination of whether the misfire has occurred using, as an input, the number of times counted by the provisional determination counting process during a specific period, 
 
 a length of the specific period is defined by a number of rotations of a crankshaft of the internal combustion engine, 
 the official determination process includes a process that makes the official determination that the misfire has occurred even in a case where a frequency at which the provisional determination of the misfire has been made in the specific period is lower when the deactivating process is executed in the specific period than when the deactivating process is not executed in the specific period, and 
 the frequency at which the provisional determination of the misfire has been made in the specific period is a value obtained by dividing a number of times the provisional determination has been made by the number of rotations of the crankshaft in the specific period. 
 
     
     
       2. The misfire detection device according to  claim 1 , wherein the official determination process includes a process that makes the official determination that the misfire has occurred even in the case where the frequency at which the provisional determination of the misfire has been made in the specific period is lower when the deactivating process is executed in the specific period a large number of times than when the deactivating process is executed in the specific period a small number of times. 
     
     
       3. The misfire detection device according to  claim 1 , wherein
 the official determination process includes, as an input, the number of times counted by the provisional determination counting process during the specific period and makes the official determination that the misfire has occurred when the number of times the provisional determination has been made is greater than or equal to a determination threshold value, and 
 the official determination process includes an extending process that sets the specific period to be longer when the deactivating process is executed than when the deactivating process is not executed. 
 
     
     
       4. The misfire detection device according to  claim 3 , wherein
 the official determination process includes a validity counting process that monitors whether the combustion control is executed in an occurrence cycle of a compression top dead center and counts a number of times the combustion control is executed when the combustion control is executed, and 
 the extending process includes a specific period setting process that sets the specific period to a period in which a valid number of times reaches a given value, the valid number of times referring to the number of times counted by the validity counting process. 
 
     
     
       5. The misfire detection device according to  claim 3 , wherein
 the official determination process includes a deactivation counting process that monitors whether the deactivating process is executed in an occurrence cycle of a compression top dead center and counts a number of times the deactivating process has been executed, and 
 the extending process increases an extension amount of the specific period as the number of times counted by the deactivation counting process increases. 
 
     
     
       6. The misfire detection device according to  claim 1 , wherein
 the official determination process includes, as an input, the number of times counted by the provisional determination counting process during the specific period and makes the official determination that the misfire has occurred when the number of times the provisional determination has been made is greater than or equal to a determination threshold value, and 
 the official determination process includes a setting process that sets the determination threshold value to be smaller when the deactivating process is executed in the specific period than when the deactivating process is not executed in the specific period. 
 
     
     
       7. The misfire detection device according to  claim 6 , wherein
 the official determination process includes a deactivation counting process that monitors whether the deactivating process is executed in an occurrence cycle of a compression top dead center and counts a number of times the deactivating process has been executed, and 
 the setting process includes a result of counting the deactivation counting process as an input and decreases the determination threshold value as the number of times the deactivating process has been executed becomes larger. 
 
     
     
       8. The misfire detection device according to  claim 1 , wherein
 the official determination process includes, as an input, the number of times counted by the provisional determination counting process during the specific period and makes the official determination that the misfire has occurred when the number of times the provisional determination has been made is greater than or equal to a determination threshold value, and 
 the official determination process includes a correcting process that corrects the number of times counted by the provisional determination counting process such that the number of times the provisional determination of the misfire has been made increases when the deactivating process is executed in the specific period. 
 
     
     
       9. The misfire detection device according to  claim 8 , wherein
 the official determination process includes a deactivation counting process that monitors whether the deactivating process is executed in an occurrence cycle of a compression top dead center and counts a number of times the deactivating process has been executed, and 
 the correcting process corrects the number of times counted by the provisional determination counting process such that the number of times the provisional determination of the misfire has been made increases as the number of times counted by the deactivation counting process increases. 
 
     
     
       10. The misfire detection device according to  claim 2 , wherein
 the internal combustion engine includes a filter that traps particulate matter in exhaust gas in an exhaust passage, and 
 the misfire detection device is configured to execute:
 a regenerating process including the deactivating process and a process that sets an air-fuel ratio in a cylinder that differs from the one or some of the cylinders to be richer than a stoichiometric air-fuel ratio when an amount of the particulate matter trapped by the filter is greater than or equal to a specific amount; and 
 a process that suspends the regenerating process in a case in which a specific condition is not satisfied after starting executing the regenerating process. 
 
 
     
     
       11. A misfire detection method for an internal combustion engine, the internal combustion engine including a sensor and cylinders, the method comprising:
 a deactivating process that deactivates combustion control for air-fuel mixture in one or some of the cylinders; 
 a provisional determination process that uses a detection value of the sensor to output a logical value indicating whether a misfire has occurred; 
 a provisional determination counting process that counts a number of times a specific one of the logical value output by the provisional determination counting process has been output; and 
 an official determination process that makes an official determination of whether the misfire has occurred using, as an input, the number of times counted by the provisional determination counting process during a specific period, wherein 
 a length of the specific period is defined by a number of rotations of a crankshaft of the internal combustion engine, 
 the official determination process includes a process that makes the official determination that the misfire has occurred even in a case where a frequency at which the provisional determination of the misfire has been made in the specific period is lower when the deactivating process is executed in the specific period than when the deactivating process is not executed in the specific period, and 
 the frequency at which the provisional determination of the misfire has been made in the specific period is a value obtained by dividing a number of times the provisional determination has been made by the number of rotations of the crankshaft in the specific period.